I noticed the same thing on my listings last night.
I use a template created with Freeform 2, and although there was a base colour for it, I used an image hosted via Photobucket for the background. The image background is what's gone, so now it just shows the base colour (rendered via HTML, rather than hosted elsewhere).
I don't know if this is an eBay issue, or a Photobucket one (if your background image was hosted elsewhere, then it would definitely be an eBay issue, though Photobucket did have scheduled maintenence last night as well, which may have broken some old links, and mine is about 3 years old...)
I'm in the process of updating my template anyway, which has a plain background, but if the issue isn't eBay related, and doesn't self-resolve, you may need to update your template with a new link to the image you use as the background.
